Metal-oxide-semiconductor (MOS) devices are faced with reliability issues that affect transistors' electrical characteristics such as drain on-current, off-current, leakage current, etc. For example, device electrical parameters including carrier mobility (μ), threshold voltage (Vth) can be degraded as the MOS device ages over time. One of the most reliability concerns in MOS devices is commonly referred to as bias temperature instability (BTI) degradation. The aging of the device can be studied, for example, by simulating the device using an electronic design automation (EDA) tool while a stress is applied to the device. Examples of stress applied to the device under simulation include bias stress and temperature stress. For instance, a device is under bias and/or temperature stress if a bias voltage or current and/or a temperature with a value higher than nominal value is applied to the device.
A conventional method of calculating BTI degradation of a device in the existing reliability prediction tools is to sum the degradations that occurred in a number of time steps during a transient analysis to find a total degradation. The total degradation is then extrapolated to a long-term period such as a defined aging time, by using a time dependent only relation, to obtain a predicted degradation value for the defined aging time. The extrapolation is often performed based on a power law or a logarithmic equation. The degradation recovery may be calculated in a similar way, or even further simplified.
Current measurement results of advanced fin field-effect transistor (FinFET) devices demonstrate that neither the stress nor the recovery degradation is following a simple mathematical function. More importantly, the degradation recovery depends on the device's degradation state that has been observed in both FinFET and conventional MOSFET devices. Therefore, the existing approach for BTI calculation cannot work for FinFET technology, which involves using more complex mathematical models. The approach for FinFET technology involves accounting for the degradation recovery dependence on the current state of degradation of devices, which can be either FinFET or MOSFET transistors.